1. Field of the Invention
This invention relates to an apparatus and method for encoding binary digital data in ternary form and has applicability to digital data communication systems and magnetic data storage systems. The invention is described herein with reference to a magnetic data storage system utilizing two level ternary data encoding.
2. Description of the Prior Art
The desirability of encoding binary data before it is recorded on a magnetic medium has been recognized and has resulted in substantial increases in the data capacity of magnetic recording systems without substantial alteration to the physical characteristics of the read/write head and/or the medium. A summary of some of the known techniques for encoding data is set forth in commonly owned U.S. Pat. No. 4,323,931, issued Apr. 6, 1982. Also summarizing various prior art binary recording techniques are articles entitled, "An Optimization of Modulation Codes in Digital Recording" by T. Horiguchi and K. Morita, IEEE Transactions on Magnetics, volume MAG-12, no. 6, Nov. 6, 1976 and "A New Look Ahead Code for Increased Data Density" by G. V. Jacoby, published in IEEE Transactions on Magnetics, volume MAG-13 no. 5, September, 1977. The above noted references summarize the progression development of codes from the so-called NRZ code to and including the 3PM code with the resultant substantial increase in the storage capacity of magnetic data storage equipment such as disk packs and the like.